dolphin pair
Dolphins mimic each others' squeaks and whistles, possibly suggesting a sophisticated kind of communication. Reuters

Scientists from the United States have found that dolphins can stay alert for 15 days or more with just one half of their brain functioning. It is an essential survival mechanism, the Press Association has reported.

Apart from allowing dolphins to come to the ocean surface for a breath of fresh air, this mechanism helps dolphins remain vigilant against sharks.

The findings published in the online journal Public Library of Science ONE reported how if dolphins slept like terrestrial animals they may drown.

Scientists in California, while testing the ability of bottlenose dolphins to echolocate accurately over extended period of time, wrote: "If dolphins sleep like terrestrial animals, they might drown. If dolphins fail to maintain vigilance, they become susceptible to predation. As a result, the apparent 'extreme' capabilities these animals possess are likely to be quite normal, unspectacular, and necessary for survival from the dolphin's perspective."

The study involved two dolphins – a male named Nay and a female named Say – that swam around a pen searching for phantom sonar targets. If a dolphin correctly detected a sound pulse from the phantom sonar device, they were rewarded with a fish and were not given any reward if they failed to detect a pulse. The study spanned three sessions of five continuous days where both dolphins reported a success rate of 99%.

However, the female dolphin seemed to outperform the male partner, and this led to extension of tests for 30 days. Despite a storm cutting short the trial after 15 days, the performance of the female dolphin continued to remain on par with expectations.

Dr Brian Branstetter, lead researcher from the National Marine Mammal Foundation in San Diego, told Press Association: "These majestic beasts are true unwavering sentinels of the sea. The demands of ocean life on air breathing dolphins have led to incredible capabilities, one of which is the ability to continuously, perhaps indefinitely, maintain vigilant behavior through echolocation."

"From an anthropomorphic viewpoint, the ability of the dolphin to continuously monitor its environment for days without interruption seems extreme. However, the biological, sensory and cognitive ecology of these animals is relatively unique and demanding," they added.